A Study On The Vegetation Cover Change In Horqin Sandy Land During The Recent 20 Years

Sandy desertification is the main type of the desertification, it is extremely as the important environment and socio-economic problems of plaguing the world today, and threat to human survival and development. Vegetation coverage is the important factor that influences the land desertification , it is a comprehensive evaluation index that describe the plant community to overlay the earth's surface , be easy to observe, and turn a close relation with the soil erosion , water losses and the land desertification. The Horqin sandy land is at the east of northern agro-grazing ecotone in our country, belonging to the monsoon margin areas, and having typical model of the environment sensitivity and vulnerability. For a long time, it was a typical area of the development of desertification in China. But since the end of the 20th century sandy desertification in the overall reversal, had once again become China's sandy land from the environmental improvement of the cases. In view of this, this paper took a typical sandy area Keerqinzuoyihouqi as an example.With the analysis and research the calculate method of the vegetation coverage , this paper showed the quantitative analysis of 1989,2000 and third period in 2007 of vegetation coverage in the Keerqinzuoyihouqi with the method of sub-pixel model for vegetation coverage estimation based on land cover classification, and prepared to find out the trend of sandy land desertification and its characteristics in recent 20 years, then analysisd the most fundamental reasons of the desertification reversing, so as to improve the environment and provide a scientific decision making for ecological protection for future. Through the study found that:1.Used sub-pixel model to monitor the vegetation coverage of the Kezuohouqi,and mean precision validation of the extraction results was 76%, practicing to express that method can be used in the extraction of vegetation coverage in Kezuohouqi. That method could take an effective way for the sandy area's vegetation coverage estimation, to meet the basic demand of the ecosystem and the climate model research;2. The vegetation coverage levels of Kezuohouqi in 2007 was that: the type of high coverage was mainly in the eastern part and in the southwest of the Daqinggou Nature Reserve, the type of medium coverage had a great advantage and a broader distribution, the type of low coverage mainly located in the northwest, and the type of no coverage mainly located at the northwest and the number of mobile sand dunes and lake areas. From the area, the type of medium coverage covered in the absolute superiority, its shared of 72%, the type of high coverage shared of 19%, the type of low coverage shared of 8% and the type of no coverage shared of 1%;3.The vegetation coverage of Kezuohouqi was complications and diverse, of each type at continuously of convert mutually. In the recent 20 years from 1989 to 2007, the type of high coverage decreased 721km~2 to 644km~2 from 1989 to 2000,but increased 2140km~2 from 2000 to 2007. The type of medium coverage increased 6455km~2 to 9126km~2 and then decreased to 8277km~2 .The other types area of the varieties kept on decreasing variety. In the spatial distribution, the vegetation coverage of the strong increase mainly concentrated in the region of the north-west and south , Mild increase almost throughout the entire region, mild decreased mainly in the eastern part , strongly reduced the relatively small region;4.From 1989 to 2000 and again to 2007, the space landscape change of Kezuohouqi's vegetation coverage grade was that the index dominance of the type of no coverage and low coverage keep on decreasing, but the type of high coverage kept on increasing, and the type of medium coverage was first increased obviously and then decreased slightly; the calculation results of the vegetation coverage rating's diversity index showed that Kezuohouqi's vegetation coverage is in the variety development stage; The whole region performanced the features that first standardization and then crusher, The spot number of the region decreased first and then increased, from 256252 patches in 1989 decreasing to 173860 patches in 2000 and then increasing to 196908 patches again in2007. Although the variety trend inconformity in the two time segment, the area variety circumstance of each type of vegetation coverage showed an ecosystem environment of that area was turning for the better gradually.5.With the analysis of vegetation coverage variety circumstance in the two segments, one was from 1989 to 2000 and the other was from 2000 to 2007, we could see that the natural factor and the humanities factor played the common role to decide the Kezuohouqi's vegetation coverage variety circumstance, but the humanities factor played a leading role. The ecological environment construction of the Kezuohouqi will still be one long-term and the arduous duty.